Transistor vehicular radio receiver operable over a range of power supply voltages



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TRANSISTOR VEHICULAR RADIO RECEIVE April -13,

United States Patent i TRANSISTOR VEHCULAR RADl RECEIVER OPERABLE (WER A RANGE F PGWER SUPPLY VOLTAG-ES .lohn S. De Merrick, Lexington, Mass., assigner to Automatic Radio Mfg. Co. Inc., Boston, Mass., a corporation of Massachusetts Filed lune 19, 1961, Ser. No. 118,062 8 Claims. (Cl. S25- 318) The present invention relates in general to radio receivers and more particularly concerns a novel fullytransistorized vehicular radio capable of operating over a range of D.C. supply voltages from 3 to 18 volts while direct-coupling supply potentials to the transistors from the vehicle D.C. system without any switching or cornponent changes whatsoever. Despite this wide range of acceptable D.C. voltage, the change in sound level output from the receiver when the supply voltage is varied over this wide range is only slightly discernable.

Automobile, truck and tractor electrical systems in current use generally operate on standard voltages of 6 or 12 volts. Although the 12 volt battery system is the standard at this time for most current vehicles, some trucks, tractors and many older domestic and newer imported automobiles still operate with .a 6 volt system.

Radios designed and manufactured for use in these vehicles can be classified in one of the following categories:

(l) Radios employing tubes, transistors, or a hybrid combination of both are suitable for use with either a 6 volt system or a 12 volt system but not both.

(2) A tube, transistor or hybrid combination radio which can be used with either a 6 or 12 volt system by manual selection with a switch or a special plug. This switch or plug alters operating parameters so that tubes, transistors or components will not be damaged when subjected to the higher 12 volt system, and provide adequate sensitivity without distortion when used with a 6 volt system.

The second system has a number of disadvantages. First, the necessity for switching introduces not only an inconvenience, but may also result in damage if a 12 volt supply is applied to the receiver with the switch in the 6 volt position. Conversely, if the receiver is connected to a 6 volt system with the switch in the 12 volt position, performance is inadequate. If the owner of the radio is unaware of the necessity for correctly positioning the switch, his dissatisfaction with the performance is generally followed by a complaint to the dealer. lf the owner realizes that the switch is incorrectly positioned, he must find the usually inconveniently located plug or switch and position it correctly. Another disadvantage resides in the requirement `for additional components, thus adding to total cost.

Since many of these receivers are installed by the eventual user and sold through mail order, these disadvantages are serious. As a result, most mail order houses carry separate models of receivers, one for a 6 volt system and the other for a 12 volt system, rather than risk the injury to their good will arising from customer dissatisfaction with an improperly installed receiver. But stocking and producing two models of receivers sacrifices economies available from mass producing and stocking a single model, thereby adding costs which the user eventually bears. Y

lt is an important object of the present invention to provide a vehicular radio receiver' having a pair of leads for receiving all its energizing power from a D.C. source and capable of satis-factory operation over an exceptionally wide range of potentials of that source, the range embracing both 6 and l2 volts.

Sdififi Patented Apr. 13, 1965 lCC lt is another object of the invention to achieve the preceding object with a fully-transistorized receiver.

It is a further object of the invention to achieve the preceding object with relatively low cost components.

It is another object of the invention to achieve the preceding while maintaining the overall receiver sensitivity relatively insensitive to the potential of the D.C. energizing source.

According to the invention, the gain of the local oscillator feedback loop is fixed so that the amplitude of the injected oscillator signal corresponds to the nominal injection amplitude for which the oscillator transistor oscillates and mixes optimally with the potential of the D.C. energizing source at a relatively low value of the range of potentials in which the receiver is operative. In addition, automatic gain control signal is injected into the Rai?. amplifier and the LF. amplifier. The audio voltage amplifier includes a biasing network comprising resistors having temperature coeicients of opposite sense so that static bias is altered closer to cutoff as the potential of the energizing source increases. The power amplifier stage includes temperature sensitive biasing means tending to lalter the bias of that stage closer to cutoff as the potential of the energizing source increases. Another feature of the invention resides in placing temperature sensitive resistors in at least some of the biasing networks described above in contact with the power transistor heat sink to enhance their sensitivity to changes in potential of the supply source.

The foregoing features coact to sustain local oscillation over a wide range of supply source potentials while maintaining the overall receiver gain constant -to a remarkable degree.

Other features, objects and advantages of the invention will become apparent from the following specification when read in connection with the accompanying drawing in which:

FfG. 1 is a schematic circuit diagram of an exemplary embodiment of the invention which operates over a range of D.C. source potentials from 3 to 18 volts; and

FIG. 2 is a view, partially in section, illustrating the physical location of certain temperature sensitive biasing resistors near the heat sink absorbing heat from the power transistor.

With reference now to the drawing and more particularly FG. 1 thereof, there is illustnated a schematic circuit diagram of an exemplary embodiment according to the invention. This schematic circuit diagram includes typical values in ohms, henries and microfarads of many resistors, inductors and capacitors, respectively. Where the values of some capacitors are designated in micromicrofarads, ,iL/Lfd. is appended to the numerical value. Since many of the circuits are in principle known sufficiently well to those skilled in the art so that the invention can be practiced from the schematic circuit diagram as supplemented by features pointed out below, known circuits will be described only generally.

A D.C. potential that may be anywhere lfrom 3 to 18 volts is applied from the vehicles electrical system between ground terminal 11 and positive terminal 12. When switch S1 is closed, the potential on terminal 12 is coupled to the six transistors TR-1-TR-6 to place the receiver into immediate operation so long as the source potential is within the stated 6:1 range of potentials. Before discussing certain features of the novel circuit which lead to this unusual performance, it is helpful to first generally consider the circuit.

Transistor TR-1 and associated circuits comprise the R.F. amplifier stage. Transistor TR-Z and associated circuit components comprise the oscillator-mixer stage. The first LF. transformer T-l couples the 1.-?. signal developed on the collector of transistor TR-2 to the I.F. amplifier stage comprising transistor 'TR-3 `and associated components. The second LF. transformer T-Z couples the amplified I.F. signal to the detector circuit comprising diode D1 and associated circuit components. Potentiometer R-i functions as a tone control. Transistor 'TR-4 and associated circuit components comprise the audio signal amplification stage, R-i'7 being the volume control. Transistor TR-S functions as an emitter follower for coupling the amplified signal from the collector of transistor TR-4 to the base of transistor TR-6. Transistor 'TR-6 and associated circuit components comprise the power amplification stage for driving the loudspeaker.

Having `briefly described the general arrangement of the receiver of FlG. l, it is appropriate to consider certain features of the invention which lead to its remarkable performance over such a wide range of electrical supply voltages. The broken lines 13 represent a mechanical linkage for simultaneously controlling the lantenna tuning inductance 14, the R.F. amplifier tuning inductance 15 and the oscillator tuning inductance 16. As is customary, inductances 14 and 15 are adjusted so that they resonate with associated capacities at the frequency of the input signal to be received. The inductance of oscillator inductance 16 is normally adjusted to produce oscillations at a frequency spaced by the LF. frequency from the signal frequency to be received. It will be observed that oscillator inductance 16 comprises primarily the secondary winding inductance of a transformer whose primary winding feeds back the energy required to sustain oscillations. it has been discovered that for an inductance 16 of 98 turns of number 842 wire upon a 0.227 inch diameter coil form, primary winding 17 is preferably 44 turns of number 8-42 wire wound over coil 16. This provides the correct degree of feedback for maintaining the amplitude of the oscillations developed across emitter resistor R at the level recommended for a transistor such as a 2N-641 when the potential on terminal 12 delivered by the vehicular electrical system is 6 volts.

A receiver according to the invention also includes a high gain AGC system including means for developing an AGC signal for application to the base of R.-F. amplifier transistor TR*1 through resistor R1 and to the base of the I.F. amplifier transistor TR-S through resistor R6. This system operates as follows. A fraction of the I.F. signal potential developed across the primary of transformer T-Z is rectified by diode D2 and delivered to the base of transistor 'TR-1 so that when the received signal is strong, a heavy bias is developed to lessen the current drawn by transistor TR-1. When transistor TR-l draws less current, the emitter potential across resistor R4 is lowered, thereby lowering the bias coupled through resistor R6 and the tapped secondary winding of transformer T-l, thereby lowering the gain of I.F. transistor TR-3.

Another important gain controlling feature has been discovered to be present in the mixer-oscillator circuit. When the potential on terminal 12 increases, the strength of the oscillations developed across emitter resistor R10 of transistor TR-Z increases to increase 4the base-emitter bias and lower the conversion gain of transistor 'FR-2. Although the gain of the audio stages tends to increase with an increase in potential on terminal 12, the reduction in gain caused by 4the AGC circuits and the oscillator tend to make the overall receiver gain relatively constant. In fact, actual measurements show that changing the potential on terminal 12 from 6 volts to 12 volts results in an increase of but two decibels in the laudio signal delivered to the loudspeaker.

Still another feature of the invention resides in introducing potential sensitive gain into the audio circuits. The means for biasing the base of transistor TR-S comprises resistors R23 and R24. By choosing resistor R23 to have a negative temperature coefficient and resistor R24 to have a positive temperature coefficient, the base-emitter biasing potential of emit-ter follower transistor TR-S becomes greater with increasing potential on terminal 12 to prevent that transistor from drawing excessive current. Emitter resistor R-28 of transistor TR- is chosen to have a positive temperature coeliicient to increase the base-emitter bias of that transistor and prevent excessive current from being drawn when the potential on terminal 12 rises. The biasing features mentioned Iabove permit the use of relatively low cost transistors in the audio aniplifier stages. Thus, transistors 'FR-4 and TR-S may be 2N-591s and transistor TR-6 may be a 2N-031.

Referring to FIG. 2, there is shown a feature of the invention for enhancing the protective action afforded by the temperature-sensitive biasing resistors. Resistors R23, R24 and R28 are shown physically adjacent fins of the heat sink for conducting heat away from power transistor 'TR-6. Transistor TR-6 draws more current with increased voltage on terminal 12. It therefore dissipates more heat to raise the temperature of the fins of the heat sink and cause the temperature-sensitive resistors to introduce their current-limiting effect-s to a greater degree more rapidly.

There has been described a novel vehicular radio re- Ceiver capable of operating over a D.-C. supply potential range of 3-18 volts. An exemplary embodiment of the invention using the transistor types described above and types Zbl-640 and Zbl-642 for transistors TR-l and TR-3, respectively, `has the following characteristics:

Potential on terminal ZZ of six volts ensitivity 6 microvolts for 1 watt output with the input signal modulated at 30%.

Potential on terminal 12 of twelve volts Sensitivity 3 microvolts for 1 watt output with the input signal modulated at 30%.

The following test was conducted with the exemplary embodiment described above. An R.F. input signal of from 50 microvolts to of the order of one volt was applied to the antenna input connector. The volume control was then adjusted until the audio output power delivered to the speaker was one watt with 6 volts on terminal 12. The potential on terminal 12 was then changed to 12 volts. The power delivered to the speaker increased by only two decibels.

It is apparent that those skilled in the art may now make numerous modifications of and departures from the specific embodiment described herein without departing from the inventive concepts. Consequently, the invention is to be construed as limited only by the spirit and scope of the appended claims.

What is claimed is:

1. A radio receiver comprising, cascaded transistorized radio receiver circuits, a terminal pair for receiving a D.-C. potential within a range embracing both first and second potentials one of which is at least twice the other, means for direct-coupling said terminal pair to all of said transistors to establish operating potentials on the. elements thereof rendering each of said circuits normally operating, one of said circuits consisting of a mixeroscillator with an associated transistor and having means for regeneratively feeding back energy at a predetermined A.-C. frequency to said mixer-oscillator transistor to maintain oscillations, the gain of said feedback means being a value sufiicient to provide energy of said predetermined A.C. frequency to both sustain oscillation at both of said two potentials while causing a reduction in the conversion gain of said mixer-oscillator transistor in response to an increase in the potential magnitude applied to said ter- .inal pair, and biasing means associated with said transistors responsive to input signal level and the potential on said terminal pair for maintaining said transistors normally operating in all said circuits at both said potentials and. within the maximum dissipative ratings of said transistors.

2. A radio receiver in accordance with claim 1 wherein Said means for regeneratively feeding back consists of a transformer having coaxial primary and secondary windings upon a coil form with a diameter of substantially 0.227, said primary winding consisting of substantially 44 turns and said secondary winding consisting of substantially 98 turns, said rst and second potentials being six and twelve volts, respectively.

3. A radio receiver in accordance with claim 1 wherein said transistorized circuits include audio amplification circuits having at least a transistor, resistance means biasing said audio circuits transistor in accordance with its resistance value, said resistance means being responsive to the D.C. potential on said terminal pair for altering said resistance value to maintain the dissipation of said audio circuit transistor normally amplifying and within prescribed maximum ratings of said audio circuit when either of said potentials is applied to said terminal pair.

4. A radio receiver in accordance with claim 3 Wherein said audio amplification circuits include a iirst transistor having at least a collector and a base, rst and second resistors having opposite temperature coefficients connected between said first transistor and a first terminal of said pair, a capacitor connected between the junction of said first and second resistors and the other terminal of said pair for providing a low impedance signal path between said junction and said other terminal, a second transistor having a base, and means for direct-coupling said second transistor base to said first transistor collector, said iirst and second resistors responding to an increase in temperature by altering the bias on the base of said second transistor in a direction tending to reduce the collector current drawn thereby.

5. A radio receiver in accordance with claim 4 and further comprising a power transistor with an emitter and a base, said second transistor having an emitter and functioning as an emitter follower, means for direct coupling said second transistor emitter to said power transistor base, and a temperature sensitive biasing resistor in series with said power transistor emitter responsive to an increase in temperature with an increase in resistance tending to reduce the current drawn by said power transistor.

6. A radio receiver in accordance with claim 5 and a heat sink withdrawing heat from said power transistor and heating said rst and second resistors and said biasing resistor.

7. An audio amplification circuit operative over a wide range of D.C. potentials delivered to a terminal pair comprising,

said terminal pair,

a first transistor having at least a collector and a base,

first and second resistors having opposite temperature coefficients connected betwen said first transistor and a first terminal of said pair,

a capacitor connected between the junction of said first and second resistors and the other terminal of said pair for providing a low impedance signal path between said junction and said other terminal,

a second transistor having at least a base,

means for direct-coupling said second transistor base to said first transistor collector,

said iirst and second resistors responding to an increase in temperature by altering the bias on the base of said second transistor in a direction tending to reduce the collector current drawn thereby,

a power transistor with at least an emitter and a base,

said second transistor having an emitter and functioning as an emitter follower,

means for direct-coupling said second transistor emitter to said power transistor base,

and a temperature sensitive biasing resistor in series with said power transistor emitter responsive to an increase in temperature with an increase in resistance tending to reduce the current drawn by said power transistor.

8. An audio amplification circuit in accordance with claim 7 and further comprising, a heat sink withdrawing heat from said power transistor and heating said first and second resistors and said biasing resistor.

References Cited bythe Examiner UNITED STATES PATENTS 2,831,114 4/58 Overbeek 330-40 2,842,669 7/58 Thomas 331--183 2,858,424 10/58 Stern et al. S25-485 2,887,574 5/59 Sciurba 325-319 DAVID G. REDINBAUGH, Primary Examiner.

ROY LAKE, Examiner. "l 

1. A RADIO RECEIVER COMPRISING, CASCADED TRANSISTORIZED RADIO RECEIVER CIRCUITS, A TERMINAL PAIR FOR RECEIVING A D.-C. POTENTIAL WITHIN A RANGE EMBRACING BOTH FIRST AND SECOND POTENTIALS ONE OF WHICH IS AT LEAST TWICE THE OTHER, MEANS FOR DIRECT-COUPLING SAID TERMINAL PAIR TO ALL OF SAID TRANSISTORS TO ESTABLISH OPERATING POTENTIALS ON THE ELEMENTS THEREOF RENDERING EACH OF SAID CIRCUITS NORMALLY OPERATING, ONE OF SAID CIRCUITS CONSISTING OF A MIXEROSCILLATOR WITH AN ASSOCIATED TRANSISTOR AND HAVING MEANS FOR REGENERATIVELY FEEDING BACK ENERGY AT A PREDETERMINED A.-C. FREQUENCY TO SAID MIXER-OSCILLATOR TRANSISTOR TO MAINTAIN OSCILLTIONS, THE GAIN OF SAID FEEDBACK MEANS BEING A VALUE SUFFICIENT TO PROVIDE ENERGY OF SAID PREDETERMINED A.-C. FREQUENCY TO BOTH SUSTAIN OSCILLATION AT BOTH OF SAID TWO POTENTIALS WHILE CAUSING A REDUCTION IN THE CONVERSION GAIN OF SAID MIXER-OSCILLATOR IN RESPONSE TO AN INCREASE IN THE POTENTIAL MAGNITUDE APPLIED TO SAID TERMINAL PAIR, AND BIASING MEANS ASSOCIATED WITH SAID TRANSISTORS RESPONSIVE TO INPUT SIGNAL LEVEL AND THE POTENTIAL ON SAID TERMINAL PAIR FOR MAINTAINING SAID TRANSISTORS NORMALLY OPERATING IN ALL SAID CIRCUITS AT BOTH SAID POTENTIALS AND WITHIN THE MAXIMUM DISSIPATIVE RATINGS OF SAID TRANSISTORS. 